Question: Solve for $x$ and $y$ using substitution. ${2x-4y = -8}$ ${y = -x-7}$
Answer: Since $y$ has already been solved for, substitute $-x-7$ for $y$ in the first equation. ${2x - 4}{(-x-7)}{= -8}$ Simplify and solve for $x$ $2x+4x + 28 = -8$ $6x+28 = -8$ $6x+28{-28} = -8{-28}$ $6x = -36$ $\dfrac{6x}{{6}} = \dfrac{-36}{{6}}$ ${x = -6}$ Now that you know ${x = -6}$ , plug it back into $\thinspace {y = -x-7}\thinspace$ to find $y$ ${y = -}{(-6)}{ - 7}$ $y = 6 - 7$ $y = -1$ You can also plug ${x = -6}$ into $\thinspace {2x-4y = -8}\thinspace$ and get the same answer for $y$ : ${2}{(-6)}{ - 4y = -8}$ ${y = -1}$